In recent years, various electronic appliances have actively been downsized, and there is a tendency of manufacturing various devices by using a thin film process along with such downsizing. Under the circumstances, as a magnetic device such as an inductor (reactor), a trance, and a magnetic head, there has been proposed a planar magnetic device (flat inductor) having a shell type structure wherein a planar coil having a spiral shape or a zigzag pattern (meander type) coated with a magnetic substance in place of a conventional structure having a bulk magnetic material provided with a coil, and attempts have been made for downsizing and thinning the device (see Non-Patent Document 1, for example).
In turn, as can be seen in an example of DC-DC converter for small electronic appliances, there is an increasing technological demand for enabling operation at a high operation frequency of a megahertz level or more in order to realize downsizing and lightweight of the appliances. Among others, a high frequency inductor serves as a key component, and the following characteristics are in demand.                (1) Small and thin (lightweight).        (2) Good frequency characteristics.        (3) Appropriate power capacity.        
As a small inductor device, in general, those obtained by winding a coil around a bulk ferrite and those obtained by integrally baking a coating type ferrite material and a coating type conductor material have been put into practical use (see Patent Document 1, for example).
The former one is increased in proportion of a surface deteriorated layer caused by process distortion due to polishing to a total volume along with downsizing and thinning of a bulk ferrite core, so that the characteristic such as a magnetic permeability are deteriorated to hamper realization of an inductor device achieving a low loss and high inductance.
The latter one is manufactured by applying a coil by patterning so as to form a spiral shape or a toroidal shape, applying the ferrite in such a manner that a soft magnetic body is excited by the coil, and baking the coil and the ferrite. For example, a toroidal type inductor is manufactured by a process of applying a ferrite and a conductor by alternate patterning.
Patent Document 1: JP-A-2002-2999120
Non-Patent Document 1: IEEE Trans. Magn. MAG-20, No. 5, pp. 1804-1806
However, among the above-described conventional inductors, the former one is increased in proportion of surface deteriorated layer caused by process distortion due to polishing to a total volume along with downsizing and thinning of a bulk ferrite core, so that the characteristic such as a magnetic permeability are deteriorated to hamper realization of high inductance device having a reduced height. Also, since magnetic permeability of the latter one is generally low, the latter one has a drawback of having difficulty in achieving a large inductance value, and there has been a limit for the height reduction of a magnetic device such as the inductor when a large amount of magnetic material is used for compensating for the drawback.